Compound metal.



B. E. ELDRED.

cmMPoUND METAL. APPLICATION FILED 0GT.26.1911,

W' 14 o@ o `/r/fL-f r'/ /ffzzhf v 0 v WP Mez UNITED STATES .PATENT OFFICE.' 1

Specification of Letters Patent.

Patented ,Dea A30, 19.13l

. Agamemnononwaar1911. sesam. 656,987.

To all whom 'it may concern:

Be i. known that I, BYnoN E. Ennnnma citizen o f the United States, residing at New York, in the county of New York and State of New York, haveinvented cert-ain new and useful Improvements in Compound Metals, ofwhic'h the following is a, specification.

This invention relates to compound metals; and it comprises a composite wire or conductor of two or more metals having compensating rates of expansion and'having a core of metal of a low rate of expansion at moderate temperatures (said core .advantageously being of nickelfsteel), firmly and permanently united by a metallic union to a sheath or sheaths of'one or more high melting metals havin 'a substantially uniform and higher rate o expansion, such as copper, gold,silverandplatinum,such oompositewire, as a Whole, having a 10W and approximately uniform rate ofexpansion; as for example, a composite wire having a nickel steel core of low expansion, an annular layer of copper Welded thereto and an annular layer of platinum Welded to the copper, the composition of the core, and, consequently, its expension, and the thicknesses of the sheath layer or layers being so correlated that the wire, as a whole, has a low, substantially uniform rate of expansion, such rate of -expansion being less than that of platinum or` less than about 00000899; and it further comprises a compound article such as an electric lamp, having a body of glass with such a wire sealed therein and with the portions of the glass next to such wireunder com ression; all as more fully hereinafter set orth and as claimed. A

Electric lamps and the like are generally provided with eading-in Wires of platinum sealed in or through their Walls; latinum having the roperty of makinga gas-tight union with used and softened glass. Platinum expands and contracts about .00000899 te .0000091 for each ceutigrade degree change in temperature, and as glassat temperatures below, Say, 100 C. can 'be obtained of an expansion as high as 0.00000810, (rising to 0.0000087v` 'or 0.0000088 at temperatures around 300 C.) a union can be formed with platinum at the softening point of such glass which in most cases will persist on cooling. The tendency of the platinum, whichl contracts more on coolin 'to shrink away from the glass is resisted" y. the mechanical strength of the union formed with the softened glass. In the cooled lamp the -layers of glass next the wire are however under tension and this may. produce cracks and air leaks. It 'has not proved practicable to substitute any other metals for platinum since all the other high melting metals have a still greater rate of expansion and none of them tends to form the same physical union with glass. Certain alloys, such as nickel steel may be produced of variousl low rates of expansion; and it has been proposed to use such an alloy having an expansion equal to that of platinum or of the standard kinds of lamp glass, though, as noted, the expansion of platinum is higher than is desirable. But in any event, these metals do not form a good physlcal union with glass, possiblypartly .l

because of their oxidizablityand partly becausel they lack the physical affinity for lass displayed by platinum. It has also een proposed to use compound wire produced by drawing down toget er a platinum tube and a contained coreof nickel-steel, iron, etc., having a coetiicient of expansion equal to that of platinum, in theattempt to maintain a good union between the platinum and the core. Aside from the fact that the rate of expansion of such a Wire does not offer any advantage as a leading-in wire, these attempts were not successful for the reason that platinum and these baser metals do not Weld together on simply heating and workt ing, but remain with their surfaces discrete; with a seam between them through which air in time will penetrate, oxidizing the core and also making the lamps leak.

- In the resent invention, I have obviated the statedp disadvantages and obtained certain new advantages by departing from the idea that the wire shall, as a whole, have substantially the same rate of expansion as platinum. Platinum, as stated, has a rate of expansion which is above that of the glasses, there being, as a matter of fact, no commercial glass with an expansion as high as that of platinum. The best glasses now in use for electric lamps showexpansions at temperatures up to 100 C. ofibout 0000081. At temperatures abone 100 C., the rate of expansion increases somewhat and at 300 C., 1t may be as high as .0000087 lso wir sealehd therein. f

.f h eexg ,lonT Q curve C Fi 1 the?" Caeiesaew-ihieiiyffhiengagihgef barsor wires one meteilfdrgcmposedofi glass, copper, nickel-steel, platinum, and theprsentfz compbsiteentire?A respe'ctiely; :asi-the.; temperature 5 increa'sess romtOe .-.to 3009i 0G. a' (linwe:-G','iI `ig: v -lgxfshowsr tlieilngthening o fg. nf,aiwvizsfofathe presentfhinvention having aan lengthnat OffCisuch that;at,f130O?;'-C..;ts lengthsis equal ato: that ofi a rod .o, lamp :glass-r also: at i300 9.-.; C; whose. length; at.0 G. is one. meter.` @Cixrve- Av :(HF ig.-:1f)sho ws therates of. ekpansion at-di terent tem eratures fior. glass suchfasis commonly use 1.'fforincandescent lamps, lwhilefx'zurvetB. .0(Eig's; 1 and-2).- is asimilar Acurve:ifors-platiiium.::Lamp glasses ofi thefitypef.:commorilysusedfsoften .at tem-J: ,f peraturesnivayingafrom aboutv 27.5.9L :.-to 39.01. i Grtandwhileithe .expansiomof glass above, this l'l temper'ature.: increases .n ra te;v this lis''; of course',v notqnaterial :'sincerit .is only', the,- rate of iexp'ansion 'f s0lid, not fluent, glassf which'.v is imp'tant Line the present ;conneo.\ t'on Atfthe 'sealingutemperatura sayO? to!V 3509- tha Aex'pansionx of. these: glasses --issutlicientl linear; that :ofi platinum 'to., insure a good oint}bt incooling to ordinary .tems peratures, thefplatinum tends ito shrink away C moreor lesslfrom the glass, its rate of contractionbeing-.greaterf This. tendency. to pull awayiisioompensated to. some extent, as stated, by-f f-the naturalC adhesion between lass andthe platinum; but :is responsible or =a`certainl numbereof 'lost lamps, :since occasionali ithe-r-:junction between :the glass andthel `latinum", which .is under strain, yieldsa'n allowsthe-` latinum-.tofpull away fromtheigla', t euse offheavywire for 'series 51am 's this ditliculty is experienced to a g'reater-exte'ntthan:in--making lamps for s'maller'currents, but' in anyrcase the loss from de fetivesealszissserious. J I `haye discoverdthat `Ican' produce a successful lampi-by4 sealing into .the glass of the'lainl')Y a composite wirewhich shall'. have, ais-a whole, arl-rate 'ofy expansion suiciently l less than'that `ofplatinum to. adapt :it `better to? glass and f lwhich, fadvantageously, ,shall have ari-expansion somewlia llesszthauthat ofthe particular lass whic beused, The'e'xpansi'orlofg-the-y Awire `x--is 5 adjusted to illforxfn' 'tothat-"f the particulanglalss to be employed y-'fsomething which is, ofcourse, 6o` impossible witha: latinum wire'hv Lemploy abonpositefl'wiiet 'avi-rigs a i core fofnickel. ste'el Tori fl'oth lowiexpansfion ahi' -h'-melting al1oy or metal. Low-expansion.; ighznieltrl glass, such as a lamp stem, with thewnew r,

T l'dm '0"''teli'f'st'f. 'ftlf- "resent'iji'ffftibiiaycomiisb u 'ri-sheailh of 'a7`liif`fh'ieltin f, substantially non-oxidizable "'i'n'rt'dfgslflifasqlltnum, covering and inlterrpfpllcyosupprted by a high-melting metal- "li'' 'dyof lower thermal expansion than th'Qglass into which the wire is sealed. icltel-teelgcan be produced whichfttftemsperatirressunderiilll@AC., has almost any rate (rf-expansion desired; even to substantially Quo expansion. Formy'ypresent purposes I prefeiyunipkelsteel ialliliave a rate Oe'tpaus' 1.1,; tite ingrat .'fietvflOO" C .ofia-pproi'i2irriately 0.000020 arat'eof course vei-y fmueh less -hanthat ofg' platinum. N-ikefsteel:feetainine sheet-.3.8. per Centof niclelanswers the urpose. very well. 'lhen'ateof expansion@ alloyslsuch as this isnot-consllfmtf. l1le. nthere,isja'fairly constantirateo exp sion freinordinary tem- .aeratunesupgta 6 0 @19.104.799 C yet above this-poing theratejofwergpangion rapidly inicreases.; there is Ewa-rdgturngi t cur/ye o expansion, at aboutf1200 C4;l asshown" in curve D, F iv. 2,

jwhere, for1convenience, the vertical sca e is zqnefhalf;thatigffligfl. In other words, an alloygwhich, atordinar Etemperatures would vhave'th`e; same rate .expansion as glass, wouldfhaveiorg'the purposes of the present 4inventiongltoo;great, an expansion at sealing temperatures. gil- It gils, therefore, necessary for thefstatedreasom and -for other reasons later appearing, ordi nari 1y to choose an alloy havingyat-ordinary temperatures, a rate of 'expansion-materially below that of glass. Theaveragecoeilicients of expansion for the 38 per cent-. allo above mentioned are approximately as.. ollows: 25-200,..0000030; 254000, 0000027. But as the. sea-l produced ata high' temperature must ersistat all lower temperatures and since t ere must not Abe too great a compressive. stress or strain in the union of the leading-iny wire. and the glass in the finished 1amp,fit isnecessary to adjust the rate of expansionat lower tem eratures. To this end, I provide the .-nielre -steel with a metallicallyunited expansion-regulatin layer of oopper,;-silver or gold or their alIoys. All three metals have a relatively high rate 0f expansion, but this rate of expansion is not farggfrom uniform orl rectilinear at all temperatures here important.- is,.;} fthe. expansion curve `for 00p er. The union between .this annularsheat or layer A rathergf, ronounced up- Curve E, Fig. 2

and; the nickelsteel core must beabsolute,

metals will lead to leakage. AS. silver Any seam or crevice between the and copper do nos form the 'wettingl .fioins'v'm tresses@ elli in...-

umon with moltenor softened glass .which is -necessary in a sealed union,

mesmo necessary to provide the composite wire with higher expansion of peintures up a sheath of 4a.. metal with which glass will form such a wetting union. In praetlce, platinumN is best adapted for this purpose. This outer layer of platinum' must be united to the co per, with av true-1 metallic union, free of' al aws, seams or defects; the two metals must be in absolute metallic union at all points between abutting surfaces. The low expansion core allows the wire, as a whole, to have the desired low aexpansion;v

'the sheathing layer of copper or like metal corrects and makessubstantially uniform the rate of ex ansion of the wire as a whole whilemat'era ly raising it above that of the core alone; and the outside layer of platinum provides for the necessary physical union with the glass. Each layer has its own function in producing -a wire of the desired characteristics; but the characteristics of each layer aremodified by reason of the presence and integral union of the various layers. The expansion of the core must be low enough to 'compensate not onl'y -for the the expansion'regulating layer of copper, but also for that of the union-securing platinum. All three layers4 must be in absolute metallic union with each other, or welded; and in practice this can only be secured by causing the intermediate layer of copper or the like to become fluid or molten Aduring the process ofA manufacture, producinga wetting union. All-layers should be free of low-melting metals such-as tin, lead and zinc to prevent injury to the platinum in making the wire and in sealing it in place.

The curve of expansion of a typical samle of wire suitable for use in my new lamp 1s shown in Fig. 1, curve C and Fig. 2, curve C. It will be seen that the expansion of the wire is not far from uniform. .The average coefiicients of Vexpansion for thisJ particular sample are as follows: 253000 eccome; .e5-200, .ooooo67; azi-100, 0000061. It is possible'to make this wire with a high-temperature coefficient as low as 0000050, but it is found in practice that it is not advisable with ordinary glasses, to go much below .0000070 With glass having an expansion coefficient of .0000081 at temt 100 C.,Ifind that a wirel aving a coefficient between .0000068 and .0000072 at'sealing temperatures gives particularly satisfactory results. With too low a coeflicient there is toostrong a contraction of the glass upon the wire, with resultantcom ression, `and a tendency to produce liedv stems, though the comparatively large mass of ,glass with its considerable elasticity is well able to withstand a reasonable strain. With heavy wires, such as are used for series "lamps,- 1t is not ordinarily practicablefto go even as low as .0000070 with the coefficient. -It should be noted that the intermediate layer of copper in this wire has a two-fold function. Mechanieall it enables a weld to be made bet-Ween the platinum and the nickel steel and it also functions in partially straightening the curve of expansion of the nickel steel and giving a wire of a more nearly constant rate of expansion. In the specific embodiment of the present invention the wire has a centralcore of low expansion metal such as nickel-steel, a surrounding expansioncoi'recting layer of copper or the like, and an exterior layer of platinum. The wire as a whole must have a rate of expansion less than that of platinum where the usual lam glass is used, or, in general, less than t at of the particular glass which is to be used for the lam s. Advantageously, this expansion will be quite substantially less than that of the glass to be used. The copper and the latinum should each form a layer of su stantial -thickness as compared with the diameter of the wire in question. In practice the platinum layer may be thinner than the copper layer. With sutliciently thick layers-of the l two metals, a substantially uniform expansion of the wire 'as a whole, is forced; and this expansion will be substantially the same for a given change of temperature not only below 100 C. but above 100 C. up to 325 C. With a wire of this type having an expansion less than that of g ass, a novel type of union is produced in sealing-in. As explained, with a platinum leading-in wire, the surrounding cohering layers of glass on cooling are under tension. With the present wire, the hot fiuent glass adjusts itself to the platinum in sealing in, and Vas the assemblage cools, the wire contracts less rapidly lthan the glass so that the glass aroundfthe wire is, so to speak, shrunk` on,

forcing 4an intimate contact in the first stages of cooling while the glass is still plastic, and later producing compression. A double advantage is thus secured. The platinum surfaceof the composite wire ives the ideal union with glass characteristic of platinum. But while in the case of an allplatinum wire the adhesive union with glass in the finished lamp is, as before pointed out, opposed by the tensile strain due to the higher expansion and contractioircoeicient of platinum, with the present composite platinum-surfaced Wire sealed in glass on the contrary, the platinum-glass adhesive union is supplemented and -perfected by the positive compressive pressure of the surrounding glass on all sides of the leading-in wire, owing to the fact that the expansion and contraction of the composite wire as a whole is lower than that ofthe glass. There is therefore much greater tendency to obtain perfect seals with the present wire than with glass and the expansion of the wire as a a wall of glass having sealed therethrough whole being not greater than that of said a composite platinum surfaced wire, said glass. wire having a lower coefficient of expansion 7. An article of manufacture comprising than said glass. and being held in thel glass 5 a body of glass and a composite wire sealed under compression.

thereinto, said wire having a 'surface layer In testimony whereof, I afiix my signaof a high-melting and substantially nonture in t-he presence of two subscribing oxidizable metal covering and internally supwitnesses. ported by a body of high-melting baser, BYRON E. ELDRED. 10 metal of lower thermal expansion than said Witnesses: v

lass. JOHN A. RILEY, 8. An article ofmanufacture comprising K. P. MCELROY. 

